Julia Roberts’ rocky relationship with her tragic half-sister took a turn for the worse last year, when the “Pretty Woman” actress accused her sibling of dishing on her to the tabloids, sources told The Post.

The Hollywood star was “mortified” when her younger sister, Nancy Motes — who was found dead earlier this week — blasted her in August to Britain’s Sun newspaper, saying, “she would tell me I was ‘definitely overweight’ . . . in a not so nice manner.”

After reading the “embarrassing” claims, sources said Roberts, 46, began to wonder if her cash-strapped sister was betraying her by selling stories to the tabloids for money.

Motes, 37, said she was not sure if Julia would be at her wedding planned for May.

“Julia didn’t get on with Nancy’s fiancé either, and had made it clear she wasn’t planning on going to the wedding,” one source said.

Motes was found dead on Sunday by her fiancé, John Dilbeck, in a bathtub filled with water.

Prescription and non-prescription drugs were found at her side in the Los Angeles home of a client for whom she had been pet-sitting. A toxicology report has not been completed but her the family said in a statement that she died of “an apparent drug overdose.”

Motes left a suicide note addressed to several family members, according to the Los Angeles County coroner’s office.

The daughter of Roberts’ mother Betty Lou and step-father Michael, Motes was raised in Smyrna, Ga., with the Oscar winner.

After Motes finished school, she followed her sister to Hollywood in 1995 with dreams of becoming an actress, but she said Roberts wasn’t supportive.

“Julia did not want to see me go down that path, mostly because I was overweight,” Motes told the Sun.

Motes’ anger toward Roberts took a more bitter turn in tweets last month, when she lashed out, “So my ‘sister’ said that with all her friends & fans she doesn’t need any more love. Just so you all know ‘America’s Sweetheart’ is a B****!!” she tweeted on Jan. 20, referring to Roberts.

“Do you want to be a fan of someone so cruel? She’s not even that good of an actress. Happy you totally ­f–ked with me?” she added in a subsequent tweet.